1. Technical Field
The present invention relates to an exposure head capable of suppressing deterioration of an image quality, an image forming device and an image forming method using the exposure head.
2. Related Art
As an exposure light source of an image forming device, there is known a device having a configuration of disposing a line head using LEDs. In Japanese Patent No. 2868175 (Document 1), there is proposed a technology for improving the resolution without decreasing the pitch of the arrangement of the light emitters in the light emitter array. FIGS. 17A and 17B are explanatory diagrams showing a schematic configuration of an image forming device using the line head disclosed in the Document 1. FIG. 17A is a diagram viewed in a direction perpendicular to a cross-sectional surface of a photoconductor 11, and FIG. 17B is a diagram viewed from a point obliquely above the photoconductor 11.
Light emitter arrays 31, 32 are arranged on a substrate 1 in n (n=2 in this example) lines, and monocular lenses 33, 34 are provided corresponding respectively to the light emitter arrays. The optical axes of the monocular lenses 33, 34 are disposed so as to be shifted from the directions towards the centers of the light beams emitted from the respective light emitter arrays 31, 32. By adopting such a configuration, the light beams from then lines of light emitter arrays can be imaged on the same line 35 of the photoconductor 11.
In the example described in the Document 1, banding is caused when the drive system of the photoconductor fluctuates (vibrates) around a predetermined printing speed or printing cycle. For example, in the case of driving with gears, velocity variation is caused in accordance with the gear pitch, which causes a striped image appearing on the image as the banding. Therefore, the problem of deterioration of the image quality has arisen. FIG. 18A shows an original image, and FIG. 18B shows the image formed on the imaging surface when the banding exists.
Further, when attaching the line head having the light emitting elements mounted thereon to the main body, the line head is sometimes fixed to the position shifted from the reference position. This condition is called skew resist misalignment, and causes deterioration of the image quality. FIG. 19A is an explanatory diagram of such skew resist misalignment. LED chips 35 each having a plurality of LED elements 36 mounted thereon are arranged linearly in an axial direction (main scanning direction) of the photoconductor to form a line head, and the line head is obliquely fixed to the main body with respect to the reference position. C.L denotes the center line of the substrate. The skew resist misalignment is also caused in the case of using organic EL elements as the light emitting elements.
Further, in the case in which LEDs are used as the light emitting elements mounted on the line head, there is caused the curvature resist misalignment in which the LED chips described above are attached to the substrate in a curved manner. FIG. 19B is an explanatory diagram of such curvature resist misalignment. Each of the LED chips 35a through 35g is mounted in a curved manner with respect to the center line C.L of the substrate except the LED chip 35b. 
In the case of mounting the LED chips on the line head, the skew resist misalignment described above and the curvature resist misalignment occur in combination. FIG. 19C is an explanatory diagram of the case in which the skew resist misalignment and the curvature resist misalignment occur in combination. As described above, since the skew resist misalignment and the curvature resist misalignment are combined, there is caused a problem that a latent image misalignment (exposure misalignment) occurs on the photoconductor to deteriorate the image quality.